Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 011754 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 155 PM EDT WED OCT 01 2014 .SYNOPSIS...WEAK HIGH PRESSURE WILL EXTEND SOUTHWARD INTO THE REGION THROUGH THURSDAY. A COLD FRONT WILL APPROACH THE MOUNTAINS FROM THE WEST ON FRIDAY... THEN SWEEP EAST ACROSS THE REGION FRIDAY NIGHT AND EARLY SATURDAY. COOL HIGH PRESSURE WILL FOLLOW THE FRONT FOR THE WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... AS OF 1200 PM WEDNESDAY... OVERVIEW: AN UPPER LEVEL LOW CENTERED ALONG THE MID-ATLANTIC COAST WILL SHIFT OFFSHORE TONIGHT AS A SHORTWAVE RIDGE OVER THE TN/OH VALLEY BUILDS EAST TOWARD THE SOUTHERN APPALACHIANS. SMALL AMPLITUDE WAVES DIGGING SOUTHEASTWARD THROUGH VA ON THE WESTERN PERIPHERY OF THE EXITING UPPER LOW COULD PROVIDE GLANCING BOUTS OF DPVA ACROSS FAR NORTHERN NC TODAY...THOUGH SYNOPTIC SUBSIDENCE WILL GRADUALLY OVERSPREAD THE REGION FROM THE WEST THIS EVENING INTO TONIGHT AS THE SHORTWAVE RIDGE PROGRESSES INTO THE SOUTHERN APPALACHIANS AND WEAK SFC HIGH PRESSURE WILL CONTINUE TO EXTEND SOUTHWARD INTO CENTRAL NC. TEMPS: DENSE FOG EARLIER THIS MORNING HAS LIFTED INTO LOW STRATUS ACROSS THE NORTHERN/NW PIEDMONT...THOUGH CEILINGS HAVE YET TO SHOW SIGNS OF MIXING OUT AND ACTUALLY APPEAR TO BE THICKENING ALONG THE I- 85 CORRIDOR...WHERE THE ADVECTION OF A SHALLOW COOL/MOIST AIRMASS SOUTHWESTWARD FROM VA INTO THE N/NW PIEDMONT HAS APPARENTLY OFFSET BUOYANT MIXING ASSOC/W INCREASING INSOLATION. ALTHOUGH LOW CEILINGS MAY PERSIST LONGER THAN ANTICIPATED (PERHAPS UNTIL 18-19Z)...THE COMBINATION OF INCREASING SUN ANGLE AND VEERING LOW-LEVEL FLOW SHOULD ALLOW CLEARING BY MID TO LATE AFTERNOON AT LATEST. WILL INDICATE SLIGHTLY COOLER HIGHS IN THE UPPER 70S ACROSS THE FAR N/NW PIEDMONT...WITH HIGHS IN THE LOWER 80S (80-83F) ELSEWHERE. PRECIP: THE LATEST NAM CONTINUES TO DEVELOP LIGHT PRECIP OVER THE NORTHERN PIEDMONT TONIGHT...THOUGH THE LATEST GFS GUIDANCE IS DRY. IT IS DIFFICULT TO ASCERTAIN WHY THE NAM CONTINUES TO DEVELOP PRECIPITATION TONIGHT GIVEN VERY WEAK LOW-LEVEL FLOW (LITTLE OR NO ADVECTION)...MARGINAL/SHALLOW MOISTURE...AND A THOROUGHLY DRY AIRMASS ABOVE 700 MB AS SYNOPTIC SUBSIDENCE INCREASES FROM THE WEST. AT THIS TIME...WILL CONTINUE TO INDICATE A DRY FCST THROUGH TONIGHT...THOUGH THERE MUST BE A PHYSICAL REASON THE NAM IS GENERATING PRECIP...SUBTLE AS IT MAY BE...AND A SLIGHT CHANCE OF SHOWERS MAY NEED TO BE INTRODUCED ACROSS THE N/NW PIEDMONT TONIGHT IN SUBSEQUENT FORECASTS. -VINCENT && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... AS OF 1200 PM WEDNESDAY... THE SHORTWAVE RIDGE WILL CONTINUE TO PROGRESS EAST ON THU... BECOMING CENTERED DIRECTLY OVER THE CAROLINAS AND VA THU AFTERNOON INTO THU NIGHT. IN THE LOWER LEVELS...WEAK SFC HIGH PRESSURE EXTENDING SOUTHWARD INTO CENTRAL NC WILL SHIFT EASTWARD IN ADVANCE OF THE RIDGE ALOFT...EVENTUALLY MOVING OFFSHORE THE CAROLINA COAST FRI MORNING AS A STRONG COLD FRONT RAPIDLY ADVANCES ACROSS THE MS RIVER INTO THE OH/TN VALLEY. GIVEN A THOROUGHLY DRY/STABLE H7-H3 LAYER ATOP SHALLOW/MARGINAL DIURNAL INSTABILITY (AT BEST) IN THE ABSENCE OF ANY SIGNIFICANT LOW OR UPPER LEVEL FORCING...WILL CONTINUE TO INDICATE A DRY FORECAST. EXPECT HIGHS SIMILAR TO TODAY...IN THE UPPER 70S TO LOWER 80S...COOLEST WHERE FOG AND LOW STRATUS PERSIST THE LONGEST PRIOR TO MIXING OUT. LOWS THU NIGHT SIMILAR TO PREVIOUS NIGHTS ALBEIT SLIGHTLY WARMER WITH THE ONSET OF A LIGHT SOUTHERLY RETURN FLOW IN THE WEST BY SUNRISE...IN THE LOWER 60S. -VINCENT && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... AS OF 155 PM WEDNESDAY... FRIDAY INTO EARLY SATURDAY... THE TIMING OF THE MAIN COLD FRONT ALONG WITH POTENTIAL CONVECTIVE OUTFLOW BOUNDARIES WILL BE THE MAIN CONCERNS FRIDAY AFTERNOON AND FRIDAY NIGHT. THEY WILL BE THE DRIVING MECHANISMS FOR SHOWERS AND SCATTERED THUNDERSTORMS. AS IT CURRENTLY APPEARS... THE MAIN THREAT OF CONVECTION SHOULD HOLD OFF UNTIL LATE IN THE AFTERNOON IN THE WEST... AND UNTIL THE EVENING IN THE CENTRAL AND EAST. SOME MODELS SUGGEST THAT THE FAYETTEVILLE TO GOLDSBORO AREAS MAY NOT SEE THE CHANCE OF SHOWERS/THUNDER UNTIL LATE EVENING AND OVERNIGHT. THERE CONTINUES TO BE QUITE A SPREAD IN THE MODELS WITH THE DETAILS OF TIMING AND QPF ASSOCIATED WITH THE FRONT... EVEN THOUGH THEY ARE TRENDING TOWARD THE AFOREMENTIONED SOLUTION. FOR NOW... FRIDAY APPEARS THAT IT WILL BE PARTLY SUNNY AND WARM WITH HIGHS IN THE LOWER 80S... EXCEPT 75-80 IN THE NORTHWEST PIEDMONT. POP WILL INCREASE FROM WEST TO EAST DURING THE LATE AFTERNOON INTO THE EVENING WITH THE TIME FRAME OF 400 PM THROUGH MIDNIGHT HIGHEST POP IN THE WEST... AND 800 PM THROUGH 400 AM HIGHEST IN THE CENTRAL AND EAST. A LEAD CONVECTIVE LINE MAY RIDE OUT AHEAD OF THE FRONT ALONG ASSOCIATED OUTFLOW BOUNDARIES... FOLLOWED BY CONVECTION ALONG THE FRONT ITSELF. QPF APPEARS TO BE ON THE ORDER OF 0.25 TO 0.50 IN THE WESTERN PIEDMONT... WITH AVERAGE AMOUNTS AROUND 0.25 IN THE SE (DUE TO WEAKENING OF THE CONVECTION DUE TO OVERNIGHT TIMING IN THE EASTERN ZONES). THE SEVERE THREAT APPEARS MINIMAL WITH ONLY MODEST INSTABILITY AND WEAK SHEAR EXPECTED. ALSO... TIMING OF THE CONVECTION FRIDAY NIGHT IN THE EAST WILL BE LATER INTO THE NOCTURNAL CYCLE... THUS THE WEAKENING TREND EXPECTED. BY 12Z/SAT... THERE MAY STILL BE A LINGERING CHANCE OF SHOWERS IN THE EAST... BUT SKIES WILL BE CLEARING FROM THE NW. THIS CLEARING TREND ALONG WITH INCREASING CAA THROUGH THE DAY WILL LEAD TO A NOTICEABLE NW BREEZE AT 10-20 MPH. IT WILL BE MUCH COOLER WITH HIGHS IN THE UPPER 60S TO MID 70S NW TO SE. SATURDAY NIGHT THROUGH WEDNESDAY... A STRONG AND COOL HIGH PRESSURE WILL BRING OUR FIRST REAL REFRESHING AIR MASS OF THE 2014 FALL SEASON SAT NIGHT INTO MONDAY. WITH MOSTLY CLEAR SKIES... LOWS WILL DIP INTO THE 40S FOR MOST OF THE REGION. HIGHS SHOULD ONLY BE IN THE MID 60S TO LOWER 70S SUN-MON. A MODERATING TREND IN TEMPERATURES IS EXPECTED TUE-WED ALONG WITH DRY CONDITIONS AS THE HIGH PRESSURE SLOWLY DRIFTS TO OUR SE THEN. LOWS WILL RETURN TO THE 50S WITH HIGHS 73-78 (NEAR NORMAL). && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... AS OF 1200 PM WEDNESDAY... 24-HR TAF PERIOD: SUB-VFR CEILINGS HAVE LARGELY MIXED OUT ACROSS CENTRAL NC AS OF 15Z...EXCEPT AT THE INT/GSO TERMINALS WHERE IFR/LIFR CEILINGS MAY PERSIST UNTIL 18-19Z BEFORE MIXING OUT DUE TO THE ADVECTION OF A SHALLOW COOL/MOIST UPSTREAM AIRMASS BY A LIGHT NORTHEAST LOW-LEVEL FLOW. EVEN AT THE INT/GSO TERMINALS...VFR CONDITIONS SHOULD PREVAIL THIS AFTERNOON/EVENING AS SUN ANGLE INCREASES AND LOW-LEVEL FLOW VEERS TOWARD THE SOUTH. BASED ON PERSISTENCE...FOG/LOW CEILINGS ARE EXPECTED TO DEVELOP AGAIN LATE TONIGHT...08-12Z THURSDAY...WITH CONDITIONS IMPROVING BY LATE THU MORNING. LOOKING AHEAD: ASIDE FROM A CONTINUED POTENTIAL FOR MORNING FOG/ STRATUS ON FRIDAY...VFR CONDITIONS WILL OTHERWISE PREVAIL. WIDESPREAD ADVERSE AVIATION CONDITIONS ARE EXPECTED FRIDAY NIGHT AS A STRONG COLD FRONT CROSSES THE CAROLINAS FROM THE WEST... ACCOMPANIED BY WIDESPREAD SHOWERS AND ISOLATED THUNDERSTORMS. VFR CONDITIONS WILL PREVAIL IN THE WAKE OF THE FRONT THIS WEEKEND AS HIGH PRESSURE BUILDS INTO THE REGION FROM THE WEST. -VINCENT && $$ SYNOPSIS...V/PWB NEAR TERM...V SHORT TERM...V LONG TERM...PWB AVIATION...V

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